Linear guide rails..flat vs round

[cloudbase]

Hi All...
I'm in the process of gathering the parts for a home hobby router..
plastics, wood, light metal etc. (24" x 36")
Am at the point of deciding on linear rails, and would like to make a
informed descision on the round guide rails vs the flat ones.
There is a lot of flat type, available out there, but my gut tells me that
a quality round style will deliver better movement...???
Anyone shedding any light on the subject, is much appreciated

Thanks
Ray

[ger21]

THK style rails can handle far greater loads than round rails, and are as smooth rolling as it gets. However, round rails can work very well on a home built machine for quite a bit less money.

[johnmac]

From what I understand, the round ones can handle misalignment, like one rail mounted slightly higher than the other, better than flat ones. (I'm not talking about an out of parallel situation.)

If flat rails are misaligned, the balls on one side of the block will carry the full load. If round rails are misaligned, the block can rotate on the rail and "self center".

I'm using flat rails on the X axis and supported round rails on the Y axis of my current build. The flat rails have plenty of specs for the maximum error permissible.

John

[ahren]

If you go with round rails, make sure you support them if they are covering any appreciable span. Unsupported round rails are the bane of many a machine builder on this forum -- they flex more than you would think (and definitely more than you want) once they get long enough.

Flat rails work well (and can be gotten cheap on ebay with patience), as do a host of other bearing methods described on this site, from V-bearings, to skate bearings to my own linear motion system. Depending on what you're looking for in terms of cost, rigidity, and accuracy, different solutions may make more sense than others for your application.

Ahren
www.cncrouterparts.com

[cloudbase]

thanx gents....and for the links.
Ahhh...the more I learn, the more I have to learn...but it's all good
Hope to post some pics as progress progresses...but there will definitely
be more questions.
I'd love to be able to see some close-ups of some of the systems that
have been a DIY for others..
Thanx again